1. Field of the Invention
The present invention generally relates to the repair of electronic circuit modules and, more particularly, to the selective removal of a single solder ball from an array of solder balls. The invention has particular application to the repair of integrated circuit (IC) chips requiring the removal of single solder balls from high density chips without damaging neighboring solder balls or the base line metal. IC chips are but one example of an electronic circuit module, and other electronic circuit modules or interconnection devices employing arrays of solder balls may be repaired using the invention.
2. Description of the Prior Art
In the functional testing of VLSI systems incorporating FLIP chip C-4 (constant controlled collapsed connector) technology, it becomes necessary to modify or customize the electrical net list to fit a particular performance criteria. These modifications are called Engineering Changes (ECs) and occur at the module level by the addition of "discrete" wire connections and the deletion of specific Logic Service Terminals (LSTs) on the top surface of the module. Prior to instituting permanent Ecs, a series of Temp Fixes are generally made to verify correct electrical functionality. Temp Fixes and ECs involve many wire adds and/or LST deletions.
A simpler way of modifying the electrical net list and specifically that of deleting or opening an electrical circuit, would be to remove the specific solder ball from the high density chip involved in the respective circuit. When the chip is subsequently joined or reflowed to the module, that circuit connection is deleted. This method does not require the deletion or opening of the LST on the module which is a permanent alteration.
Currently, there is no method for removing solder ball connectors without a high risk of damaging adjacent solder balls or the base line metal (BLM). Mechanical devices used to remove solder balls, such as scalpel or knife, often remove more than one ball and damage the BLM.